Etiquette are the rules for proper expected behavior as inscribed in a book. Decorum is how they are interpreted plus some unwritten rules. For most workplace situations, they're interchangeable. If you search for "business etiquette", you'll find plenty of books on general practices and specifics for various countries and regions. They're like a translation dictionary. It can help you learn the language, but can't help you act like a local.
When my parents and I arrived in the USA in 1953, we were seriously worried that our European mannerisms and behavior would identify us a communists and subject us to possible deportation by Joe McCarthy and his committee. It was therefore important that we look and act like genuine Americans. In public, we spoke only English, and alternately juggled the knife and fork while eating. To assist in the process, my parents purchased a book on formal dinner etiquette by Emily Post. We emulated the dinner style at home in the book on the assumption that this was the way Americans normally lived and ate. It was a big surprise when we discovered this was not the case. This should illustrate the dangers of practicing etiquette by the book.
There are also rules if etiquette which are not usually inscribed. In
1975, we were in Japan for a business meeting. After several hours of polite discussion about everything except the purpose of the meeting, we were getting nowhere. The Japanese managers were intentionally avoiding any topics related to the meeting purpose. We were getting nowhere, so they invited us to a bar to "relax". Once everyone was thoroughly inebriated, the purpose of the meeting was discussed and rather rapidly settled to everyones satisfaction. Do they need to be drunk in order to make a business decision? Apparently yes, if they want to have a face saving exit strategy should something go wrong. Being drunk when making a decision is deemed an acceptable excuse for faulty judgment. This should illustrate the danger in not knowing how the unwritten rules of etiquette are actually played.Understanding your foreign colleagues can be a problem. During interviews, I could not get any of the Japanese engineers to describe what they had accomplished. They were afraid that describing their work, without reference to the team, would in some way be disrespectful to the rest of the team. Fear of admitting failure can be a problem. I worked with some Chinese engineers who were very secretive and allowed no one to see their work. I could sense that they were having a problem, but they refused my offers of assistance. Near the end, it was obvious that they were stuck, but would pretend that everything was fine. It was then that management asked for a demonstration and the problems were revealed. They left, never admitting that they had failed, and I inherited the task of trying to patch things together. I suspect design reviews have become more popular because of problems like this. Other engineers would simply stop working when they ran into a problem because admitting that there was a problem was not acceptable. Another group specialized in extorting as much money as possible by withholding key parts of a design until the money was paid. Knowing your colleagues motivations is critical.
My guess(tm) is that you've been selected to accompany a VIP on some international business travel and are being asked simultaneously understand multiple cultures at the same time, so as not be an embarrassment to the VIP. Your question is a rather messy affair, full of comma splices, and far longer than necessary. That tells me that you are uncertain about what to ask for, what is about to happen, and what is expected of you. I suggest you speak with whomever you are replacing, and pump them for as much detail as you can digest.
Whatever you do, do NOT assume that what you see in foreign movies is typical behavior. At best, movie etiquette is distorted. At worst, it is pure fiction. When my family bought our first TV, we assumed that proper middle class behavior was exemplified by the "Ozzie and Harriet" TV show. I never could deduce how Ozzie provided an income since he never seemed to be working at a job.
Also, do NOT assume that everyone shares your values and ethics. For example: What is the difference between a bribe and a commission? The answer is simple. They're the same except a bribe is paid in advance while a commission is paid after. In western culture, a bribe is considered really bad business practices. However, in many cultures, middlemen do not want to risk their profits on one party paying a commission. So, they insist on a getting their profits in advance, also known as a bribe. (Think about that when you obtain a bank loan, and the bank asks for their "points" in advance).
Anyway, when it comes down to you properly performing as a "personal assistant", knowing how to act in accordance with the rules of etiquette and decorum will be marginally useful. They're good for when you need help making a decision. For example, an engineering code of ethics: More important will be knowing why people act that way, what motivates them to act that way, and what they expect from you. You may want to hire some local help to help you past the initial shock.
Good luck.